The use of polytetrafluoroethylene ("PTFE") as a bearing material in sleeve bearings with metallic bearing jackets or other metallic supporting layers has been proposed. For example, in U.S. Pat. No. 3,033,623 entitled "Fluorocarbon Sleeve Bearing" there is disclosed a PTFE bearing with a metal housing that consists of a housing or body that has a bore within which is disposed a readily removable sleeve of substantially uniform thickness over its bearing area. The sleeve, of a laminated construction, is provided with the surface of a wear resistant synthetic plastic having a low coefficient of friction such as PTFE. This wear resistant synthetic plastic forms a thin layer and is firmly anchored to a circumferentially rigid metallic supporting layer or sheet which is sufficiently radially flexible so that the bearing bore diameter and roundness are governed by the diameter and shape of the housing bore. The metallic backing for the wear resistant synthetic plastic having a low coefficient of friction is of such a thickness that it is circumferentially rigid when formed into a cylinder and disposed in the bore of the housing so that assurance is had that neither portion of the laminated liner will wrinkle or bunch in a circumferential direction during operation or be otherwise transformed when enclosed between the shaft and the housing. The metallic backing is sufficiently flexible that it accurately conforms to the surface of the bore and the housing thereby assuring good heat dissipation from the wear resistant synthetic friction surface and also obtaining the accurate dimensioning of the housing bore.
However, in these conventional PTFE bearings when subjected to the substantial operating load pressures common to the rotary shaft sleeve bearing of a fluid control valve, the PTFE bearing surface yields at its cold flow point (approximately 500 psi or 3448 Kpa at system temperatures of 450.degree. F. or 232.degree. C.) and extrudes from between the metal bearing jacket and the valve shaft causing the bearing to fail.
Further, in such prior PTFE bearing construction there is a strong likelihood that during normal operation of the fluid control valve, the metallic backing or housing members of the PTFE bearing will contact the rotary shaft of the fluid control valve causing scoring, seizing or otherwise harming of the shaft. The result will then be reduced valve performance or failure.
It is otherwise known in the art to manufacture sleeve-type bearings for the rotary shafts of fluid control valves entirely from polyetheretherketone ("PEEK"). While such manufacture evades the rotary shaft damage problem when the bearing is subjected to high operating load pressures, such bearings exhibit inferior coefficients of friction and wear resistance characteristics.
Accordingly, it is desired to provide a bearing for the rotary shafts of fluid control valves that is easy to use and has reduced friction, reduced cost, good chemical inertness, improved bearing load capacity and improved operational life characteristics.